Statistical aerosol properties associated with fire events from 2002 to 2019 and a case analysis in 2019 over Australia

Abstract

Abstract. Wildfires are an important contributor to atmospheric aerosols in Australia and could significantly affect the regional and even global climate. This study investigates the impact of fire events on aerosol properties along with the long-range transport of biomass-burning aerosol over Australia using multi-year measurements from Aerosol Robotic Network (AERONET) at 10 sites over Australia, a satellite dataset derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP), reanalysis data from Modern-Era Retrospective analysis for Research and Applications version 2 (MERRA-2), and back-trajectories from the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model. The fire count, fire radiative power (FRP), and aerosol optical depth (AOD) showed distinct and consistent interannual variations, with high values during September–February (biomass-burning period, BB period) and low values during March–August (non-biomass-burning period, non-BB period) every year. Strong correlation (0.62) was found between FRP and AOD over Australia. Furthermore, the correlation coefficient between AOD and fire count was much higher (0.63–0.85) during October–January than other months (−0.08 to 0.47). Characteristics of Australian aerosols showed pronounced differences between the BB period and non-BB period. AOD values significantly increased and fine-mode aerosol dominated during the BB period, especially in northern and southeastern Australia. Carbonaceous aerosol was the main contributor to total aerosols during the BB period, especially in September–December when carbonaceous aerosol contributed the most (30.08 %–42.91 %). Aerosol size distributions showed a bimodal character, with both fine and coarse aerosol particles generally increasing during the BB period. The megafires during the BB period of 2019/2020 further demonstrated the significant impact of wildfires on aerosol properties, such as the extreme increase in AOD for most of southeastern Australia, the dominance of fine particle aerosols, and the significant increase in carbonaceous and dust aerosols in southeastern and central Australia, respectively. Moreover, smoke was found to be the dominant aerosol type detected at heights from 2.5 to 12 km in southeastern Australia in December 2019 and at heights from roughly 6.2 to 12 km in January 2020. In contrast, dust was detected more frequently at heights from 2 to 5 km in November 2019 and January and February 2020. A case study emphasized that the transport of biomass-burning aerosols from wildfire plumes in eastern and southern Australia significantly impacted the aerosol loading, aerosol particle size, and aerosol type of central Australia.

Observed slump of sea land breeze in Brisbane under the effect of aerosols from remote transport during 2019 Australia mega fire events

“…The 2019 Australia mega fires occurred mainly in the eastern and southeastern coastal areas of Australian continent (Yang et al, 2021). The southeastern parts, including the State of Victoria and southeastern part of the State of New South Wales, belong to Marine Climate where obvious existence of SLB (OE-SLB) is not clearly verified because of the influence of strong westerlies and water vapor accompanied with westerlies from the ocean (Shen et al, 2021).…”

“…This could help analyze the transport effect of background wind fields on aerosols at this site. The simulated levels at the site were 500 m and 3 km since the lower level of atmosphere (500m) was closer to fire spots and there was also accumulated smoke at 3 km in the southeastern parts of Australia during the exact same month (Yang et al, 2021). The TrajStat module of Meteoinfo version 2.4.1 was also used to cluster the back trajectories based on the Euclidean distance method, whose details and source code could be found at its official website (http://meteothink.org/docs/trajstat/index.html, last access: 31 January 2021).…”

“…It can be seen that fire spots scattered all over the eastern part of Australia over the years during January. January is the middle of Australian summer which is the season when wild fires are the most frequent (Yang et al, 2021). Apart from 2020, other years also witnessed considerable scattered fire spots all over the coastal and inland regions.…”

“…Carbonaceous aerosol contains black carbon (BC) and organic carbon (OC) and serves as a major radiation-influencing aerosol which mainly comes from biomass burning (Vermote et al, 2009, Yang et al, 2021. There have been studies addressing the importance of BC on atmospheric warming and that of OC on weakening in situ downwelling solar radiation (Jacobson, 2001;Ramana et al, 2010).…”

“…have been carried out since their outbreak from different aspects. For example, Yang et al (2021) examined the statistical properties of aerosol properties associated with 2019 Australia mega fire events in both horizontal and vertical directions. Torres et al (2020) investigated the aerosol emissions during the mega fires happening in New South Wales, Australia and found a great amount of carbonaceous aerosols in the stratosphere.…”